1. Field of the Invention
This invention relates to a clutch and a method for operating such a clutch.
2. Description of Related Art
Operation of a generic clutch is influenced by the properties of the spring mechanism, among other things. The spring force produced by the spring mechanism can vary due to the manufacturing or can be varied as a function of operating time.
A power-shift transmission such as an infinitely variable, automatic power-shift transmission for vehicles having a generic clutch is known from German Patent DE 198 22 193 A1, which is a hydrodynamically operated multi-disk clutch. The closing force of this clutch is generated by a hydraulic cylinder which actuates a piston acting on the clutch disks against the force of a plate spring. The opening force is applied by the plate spring as a spring device of this clutch. The opening of the clutch, which is produced by the plate spring, must occur during an accurately predetermined period of time, i.e., within a certain time window, for optimum functioning of the shift transmission. To this end, the hydraulic pressure within the hydraulic cylinder, which is responsible for the closing of the clutch, is monitored by pressure sensors and used as control and/or regulating variables for the operation of the clutch. The measured values obtained by the pressure sensors depend on the temperature, among other things, due to the change in viscosity of the hydraulic fluid.
U.S. Pat. 5,641,048 A describes a friction clutch in which a pressure valve is spring loaded, whereby the contact pressure emanating from the spring is detected. To equalize wear on a friction clutch, a readjusting device is provided, operated as a function of the detected contact pressure of the spring for pressure equalization. The readjusting device should not be actuated during clutch operation, but instead preferably when the clutch is at standstill or possibly still in a low rpm range, which is below the rpm range in conventional clutch operation. With the device known in the past, blocking devices are provided in particular to safely prevent adjustments by the readjusting device during operation of the clutch.
German Patent DE 101 61 205 A1 describes a clutch in which the clutch pressure piece is moved by the force of a plate spring that can be displaced between an engaged position and a disengaged position. This plate spring is provided with an adjusting device by means of which a readjustment is possible to compensate for wear on the clutch. The adjustment device is equipped with a sensor by which the need for a readjustment and the extent thereof are detected.
The clutch known from German Patent DE 101 08 186 A relates only to a readjustment device for a clutch.